Lifecycle binding

[BulatMukhutdinov]

in CameraFragment you call

CameraX.bindToLifecycle(this, preview, imageCapture, imageAnalyzer)

meaning you bind it to fragment's lifecycle. But you call this method on onViewCreated() which means you would receive the old lifecycleOwner. To avoid crashing you every time also call CameraX.unbindAll() which is some sort of work around.
Instead it would be better to call CameraX.bindToLifecycle() with viewLifecycleOwner. Then you can delete CameraX.unbindAll()

Thus, it seems like you have misused fragment's lifecycle with view's lifecycle. Correct me I am wrong.
Thanks

[owahltinez]

I'm not sure what you mean by "the old lifecycleOwner". The current sample is using the fragment's lifecycle, which usually is the same as the view's lifecycle except CameraFragment sets the retainInstance flag.

By attaching CameraX to the fragment lifecycle, we avoid CameraX being fully torn down (and thus closing the camera) upon config changes like rotation. The intent is to allow for CameraX to maintain some of its state by doing: CameraX.unbindAll() → CameraX.bindToLifecycle(), which happens during onViewCreated.

By using the view's lifecycle, the order of events is: CameraX *teardown* → CameraX *initialize* → CameraX.bindToLifecycle(). However, I just tested this and it seems that this results in snappier transitions during device rotations on a Pixel 3 device. I'm guessing it's due to the teardown starting as the view gets destroyed, rather than doing everything during onViewCreated.

I will investigate the potential implications of switching to the view's lifecycle. It's likely that devices with slow camera open/close will have degraded performance using this path. We have to take into consideration other things such as navigation, multi-window environments, etc.

[BulatMukhutdinov]

Could you please explicitly specify where in the sample CameraX *initialize* happens?

[owahltinez]

CameraX initialization is not triggered by app code. Some of it happens upon app startup, some of it when the first use case is bound. It's up to the CameraX library and subject to change in the future.

[BulatMukhutdinov]

Then, returning to original question, it seems that if you would bind to fragment's lifecycle the call stack is
CameraX *initialize* → CameraX.unbindAll() → CameraX.bindToLifecycle() → (rotate) → CameraX.unbindAll() → CameraX.bindToLifecycle()
While with viewLifecycleOwner it is
CameraX *initialize* → CameraX.bindToLifecycle() → (rotate) → CameraX.bindToLifecycle()

The main concern is when you doing CameraX.unbindAll() the concept of lifecycle awareness is lost since you bind and unbind it each time manually.

[owahltinez]

While with viewLifecycleOwner it is
CameraX initialize → CameraX.bindToLifecycle() → (rotate) → CameraX.bindToLifecycle()

I don't think this is entirely true. I'm counting camera open as CameraX *initialize* although maybe I'm not making things very clear. Essentially, by binding to the view's lifecycle, we will be closing and reopening the camera every time we rotate. Whereas binding to the fragment's lifecycle we can even keep some use cases bound across config changes (which we aren't doing yet).

The main concern is when you doing CameraX.unbindAll() the concept of lifecycle awareness is lost since you bind and unbind it each time manually.

That's fair feedback, although only partly true. We are just making sure that no other use cases are bound, which is not necessarily a bad practice but, as you say, it kinda defeats the point of making everything lifecycle-aware.

As I said earlier, we will investigate switching to using the view's lifecycle as the owner. Personally, assuming there are no major drawbacks, I think it would be the right choice. It simplifies the code and sets a good example for developers to follow. Otherwise, we are chasing diminishing returns for a slight performance gain, whereas some of the optimizations could be done by CameraX itself. For example, CameraX could wait a bit to close the camera during a config change, since it's likely that an app will bind the same use cases and open the same camera again.

[BulatMukhutdinov]

Thank you for your response. I close the issue but pls ping me if there would be any updates on this